1. Field of the Invention
The present invention relates to protection of copyrighted data on a disk, and more particularly, to a method and apparatus for generating a burst cutting area (BCA) on a disk to prevent unauthorized copying, and an information storage medium having the BCA.
2. Description of the Related Art
As write-once disks or rewritable disks are widely used, copyrighted data may be copied illegally. In order to prevent illegal copy of a disk, there is a burst cutting area (BCA) in a digital versatile disk (DVD). FIG. 1 is a diagram showing a BCA of a DVD 10. Referring to FIG. 1, it can be seen that a BCA 20 is formed along the innermost track of the DVD 10 corresponding to an angle of about 330 degrees. The BCA 20 of a DVD-read only memory (ROM) or a DVD-random access memory (RAM) is formed when the DVD 10 is manufactured in a factory. By applying a pulse laser light of yttrium-aluminum-garnet (YAG) to the DVD 10, a stripe of a reflection film, which is formed inside of the DVD 10 and is made of aluminum and so on, is removed in a radial shape such that a stripe (barcode) is formed along the innermost track. Here, the stripe indicates, for example, an identification (ID) number and other identification information and additional information such as an encryption key.
FIG. 2 is a diagram to explain phase encode (PE) modulation. Referring to FIG. 2, phase modulation in which data bits change according to the locations of a mark and a space is shown. Referring to FIGS. 4A and 4B to be explained later, data bit “0” is converted into channel bit “10”, and data bit “1” is converted into channel bit “01”.
FIGS. 3A and 3B are diagrams showing examples of a frame sync pattern used in the PE modulation of FIG. 2. In the PE modulation, channel bits changes at the center of two channel bits indicating a data bit, and therefore, marks or spaces do not occur continuously for 3 or more channel bits in the case of data bits. Accordingly, a sync pattern indicating a sync bit (frame sync) can be formed by arranging continuous marks or continuous spaces in 3 or more channel bits.
FIGS. 4A and 4B are diagrams showing an example of modulating disk ID data bits by using 4-1 modulation. The 4-1 modulation is a method to modulate 2-bit data into 7 channel bits. The first 3 channel bits form a sync part expressed as “010”, and the following 4 channel bits form a data part in which data is represented by a position of “1” changing within the 4 channel bits. When 2 data bits before modulation are “00”, “01”, “10”, and “11”, the data parts are “1000”, “0100”, “0010”, and “0001”, respectively. The 7 channel bits obtained by adding the sync part and the data part and it become a word.
FIGS. 5A and 5B are diagrams showing an example of a sync pattern of a frame sync used in the 4-1 modulation of FIGS. 4A and 4B. In the 4-1 modulation, the position of logic “1” is fixed in the sync part of 3 channel bits. Accordingly, the interval of every second logic “1” occurring in a sync part is always 7. Therefore, a sync pattern can be formed by breaking the regularity of interval of every second logic “1”.
However, as the size of a disk is continuously decreasing, and therefore a starting radius for recording or reproducing data is also decreasing, the recording density of a BCA at an inner side of an optical disc should be increased.